Palladium‐Catalyzed Trifluoroethylation of Benzo[h]quinoline Derivatives by Mesityl(2,2,2‐trifluoroethyl)iodonium Triflate

Reactions of a dimeric [(bzq)Pd(OAc)]2 complex (1 a′) and mesityl(2,2,2‐trifluoroethyl)iodonium triflate (2 a) with or without additives at room temperature gave 10‐(2,2,2‐trifluoroethyl)benzo[h]quinoline rapidly in moderate to high yields. The reaction might proceed through a unstable binuclear “PdIII−CH2CF3” intermediate (I), which was likely formed in situ from the oxidative addition of 2 a to [(bzq)Pd(OAc)]2 and favorably transformed to mononuclear “(bzq)PdIV−CH2CF3” complexes (III) in the presence of another equiv.alent of 2 a and a suitable additive. Based on these, a Pd‐catalyzed C−H trifluoroethylation of benzo[h]quinolines with 2 a was developed. Numerous benzo[h]quinoline derivatives reacted with [MesICH2CF3][OTf] at room temperature in the presence of 10 mol% Pd(OAc)2 and 2 equiv.. NaHCO3 to provide the corresponding 10‐trifluoroethylated products in excellent yields. Optional additive: A mild and convenient Pd‐catalyzed C−H trifluoroethylation of benzo[h]quinolines with mesityl(2,2,2‐trifluoroethyl)iodonium triflate was developed based on the stoichiometric reactions of a dimeric [(bzq)Pd(OAc)]2 complex and the triflate, which might proceed through an unstable binuclear “PdIII−CH2CF3” intermediate, likely formed in situ and favorably transformed to mononuclear “(bzq)PdIV−CH2CF3” complexes in the presence of an excess amount of the iodonium triflate and a suitable additive.